1. Field of the Invention
The present invention relates to a magnetic recording medium which is classified into patterned media, a method of fabricating the magnetic recording medium, and a magnetic recording apparatus in which the magnetic recording medium is installed.
2. Description of the Related Art
In the modern information society, the amount of data, which is recorded on recording media, has been increasing more and more. To keep up with the increase in amount of data, there has been a demand for a recording medium and a recording apparatus with a dramatically increased recording density. As regards hard disks for which there is an increasing demand as large-capacity, inexpensive magnetic recording media, it is said that a recording density of 1 terabits per square inch or more, which is about ten times higher than a current recording density, will be required several years after.
In a currently available hard disk, recording of one bit is effected on a certain region of a magnetic recording layer formed of a polycrystalline material including fine magnetic particles. In order to increase the recording capacity of the hard disk, it is necessary to decrease a recording mark size usable for one bit so as to increase the recording density. However, if the recording mark size is simply decreased, the influence of noise will not be negligible. On the other hand, if the size of each magnetic particle is decreased, a problem of thermal fluctuation occurs, and recording cannot be maintained at ambient temperature.
To avoid this problem, patterned media have been proposed. In the patterned media, a recording material is separated by a non-recording material in advance, and recording/reproduction is performed by using each dot-like particle of recording material (recording dot) as one bit.
The patterned media are designed on the assumption of a recording density of several-hundred gigabits per inch. Accordingly, the size of a recording dot of one bit becomes several-ten nm or less. Conventionally, it has been thought that electron-beam lithography or focused ion beam lithography may be applied as a method of forming such a fine pattern on a substrate. However, to fabricate patterned media by these lithography techniques is not practical in terms of processing time and cost.
In order to fabricate patterned media at low cost in a short time period, the following methods have been proposed: (1) a method in which dot-like fine particles are arrayed on a substrate, and a magnetic material is patterned by using the fine particles as a mask; (2) a method in which a magnetic material is filled in anodized alumina nano-holes; and (3) a method in which a self-assembling phase-separated structure of a block copolymer is used to pattern a magnetic material. Each of these methods enables to pattern the substrate at a time on the entire surface thereof. However, these methods cannot control the orientation of the patterns. Thus, a microstructure having a regularly arrayed pattern can be formed microscopically. However, since many such microstructures are formed at random, defects and grain boundaries are formed at interfaces between the microstructures. When the entire substrate is observed, the orientations of arrayed patterns become irregular.
To avoid this problem, it is thought effective to define recording regions by forming guide patterns having predetermined orientation, such as a linear or lattice-shaped protruded structure, on the surface of the substrate (JP-A 2002-279616 (KOKAI) and JP-A 2002-334414 (KOKAI)). The guide patterns are formed in accordance with isolation regions which surround and separate recording regions. If a self-assembling phenomenon takes place in the recording regions under the condition that the guide patterns are formed, dot-patterns of a self-assembling material are arrayed along the guide patterns. Moreover, by transferring the dot-patterns of the self-assembling material to a magnetic material, it becomes possible to form regularly arrayed recording dots. If the recording dots are formed by making use of the guide patterns, the patterns which are regularly arrayed on the entire substrate can be formed. Therefore, it is possible to expect that read/write can exactly be performed on each dot of the obtained patterned media by a read/write head of a magnetic recording apparatus.
In the meantime, the recording dots need to have read-only recording dots, on which address data for recording regions, for instance, are written. However, as regards the patterned media in which all recording dots are regularly arrayed, it has been found that such a problem arises that write errors on the read-only dots tends to easily occur.